From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753193Ab1JJQnp (ORCPT ); Mon, 10 Oct 2011 12:43:45 -0400 Received: from mail-qy0-f174.google.com ([209.85.216.174]:47844 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753183Ab1JJQno (ORCPT ); Mon, 10 Oct 2011 12:43:44 -0400 Date: Mon, 10 Oct 2011 09:43:39 -0700 From: Tejun Heo To: Mike Galbraith Cc: LKML , Li Zefan , Paul Menage , Peter Zijlstra , David Rientjes , Thomas Gleixner , Steven Rostedt Subject: Re: [patch] cpusets, cgroups: disallow attaching kthreadd Message-ID: <20111010164339.GA8100@google.com> References: <1316758874.7393.2.camel@marge.simson.net> <4E7C2E7F.40307@cn.fujitsu.com> <1316762345.8168.4.camel@marge.simson.net> <1316770936.6641.11.camel@marge.simson.net> <1316775204.7562.9.camel@marge.simson.net> <1316788392.6544.33.camel@marge.simson.net> <1318224892.6161.45.camel@marge.simson.net> <1318233815.6527.5.camel@marge.simson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1318233815.6527.5.camel@marge.simson.net> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, (cc'ing Thomas and Steven and quoting whole body) On Mon, Oct 10, 2011 at 10:03:34AM +0200, Mike Galbraith wrote: > On Mon, 2011-10-10 at 07:34 +0200, Mike Galbraith wrote: > > Maybe the below (which seems to have been stillborn) should be done to > > cgroups as well. Postmortem: kthreadd is attached to a cgroup with no > > rt_runtime allocated, gives birth to severely handicapped kstop threads, > > humongous crash dump follows. > > > > Fiddling with kthreadd is user error, but since it makes no sense to > > move the thing, why not just say no, and save the user's toes some > > needless wear and tear. > > > > > If cpusets doesn't want to let PF_THREAD_BOUND threads out, how about > > > cpusets not letting userland scripts attach kthreadd instead? > > > > > > cpusets: disallow moving kthreadd into a cpuset. > > So how about this, both dirt simple and effective. > > cpusets, cgroups: disallow attaching kthreadd > > Allowing kthreadd to be moved to a non-root group makes no sense, it being > a global resource, and needlessly leads unsuspecting users toward trouble. > > 1. An RT workqueue worker thread spawned in a task group with no rt_runtime > allocated is not schedulable. Simple user error, but harmful to the box. > > 2. A worker thread which acquires PF_THREAD_BOUND can never leave a cpuset, > rendering the cpuset immortal. > > Save the user some unexpected trouble, just say no. > > Signed-off-by: Mike Galbraith Yes, I think we need something like this. wq workers were using PF_THREAD_BOUND to prevent diddling from userland which made some unhappy. Maybe we need a flag to properly indicate "don't diddle with this thread from userland"? But, then, mainline kernel wouldn't need the current PF_THREAD_BOUND at all. Peter, Steven, what do you think? Thanks. > --- > kernel/cpuset.c | 6 ++++-- > kernel/sched.c | 9 +++++++++ > 2 files changed, 13 insertions(+), 2 deletions(-) > > Index: linux-3.0-tip/kernel/cpuset.c > =================================================================== > --- linux-3.0-tip.orig/kernel/cpuset.c > +++ linux-3.0-tip/kernel/cpuset.c > @@ -59,6 +59,7 @@ > #include > #include > #include > +#include > > /* > * Workqueue for cpuset related tasks. > @@ -1382,9 +1383,10 @@ static int cpuset_can_attach(struct cgro > * set of allowed nodes is unnecessary. Thus, cpusets are not > * applicable for such threads. This prevents checking for success of > * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may > - * be changed. > + * be changed. We also disallow attaching kthreadd, to prevent it's > + * child from becoming trapped should it then acquire PF_THREAD_BOUND. > */ > - if (tsk->flags & PF_THREAD_BOUND) > + if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task) > return -EINVAL; > > return 0; > Index: linux-3.0-tip/kernel/sched.c > =================================================================== > --- linux-3.0-tip.orig/kernel/sched.c > +++ linux-3.0-tip/kernel/sched.c > @@ -9132,6 +9132,15 @@ cpu_cgroup_destroy(struct cgroup_subsys > static int > cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) > { > + /* > + * kthreadd can fork workers for an RT workqueue in a cgroup > + * which may or may not have rt_runtime allocated. Just say no, > + * as attaching a global resource to a non-root group doesn't > + * make any sense anyway. > + */ > + if (tsk == kthreadd_task) > + return -EINVAL; > + > #ifdef CONFIG_RT_GROUP_SCHED > if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk)) > return -EINVAL; > > -- tejun